Randomly Intermittent Thoughts » Programming

How do you ‘svn delete’ missing working copy files?

nblom — Fri, 15 Oct 2010 18:27:25 +0000

Recently, I was upgrading a set of files in a svn working copy directory. I received the upgraded files from a third party. I used a merge tool to synchronize and merge the files, deleting files that were no longer needed. But this just deleted them from the working copy; not the svn repository. I could do a 'svn status' and "see" that files were missing, but there didn't seem to be a way for me to tell svn to delete them.

A quick Google Search pointed me to SNIPPLR.

The batch file created by troy, helped enormously!
I modified it a bit to fit my system. See below.

PLAIN TEXT

@echo off
rem :: This script deletes files from svn that are missing in the specified working copy.
set SVN=\bin\svn.exe
if "%1"=="" (
echo usage: %0 workingCopy
exit /b
)
for /f "usebackq tokens=1*" %%a in (`%SVN% status %1`) do (
if "%%a"=="!" (
echo svn delete "%%b"
%SVN% delete "%%b"
)
)

Edit: Fixed a problem with the actual svn delete command. It wasn't wrapped in %s so it was actually calling a SVN executable in my path. I recently had to replace a hard drive so when I went to run this batch file, svn wasn't in this new system's path and failed.

Final Static Objects = the Devil

nblom — Thu, 03 Sep 2009 21:51:22 +0000

What does this code output?
No fair, running it!

PLAIN TEXT

public class Hmm {
public static class X{
int x = -1;
public X(){}
public X(int x ){setX(x);}
public int getX(){return x;}
public void setX(int x){this.x = x;}
}
// the default object has a default value of 0.
public final static X DEFAULT_X = new X(0);
private X m_X = new X();
// A Hmm object uses the default value
public Hmm(){
m_X = DEFAULT_X;
}
public X getX(){
return m_X;
}
public void setX(X x){
this.m_X.setX(x.getX());
}
public static void main(String[] args){
Hmm hmm1 = new Hmm();
hmm1.getX().setX(15);
Hmm hmm2 = new Hmm();
System.out.println("Hmm1 X = " +
hmm1.getX().getX());
System.out.println("Hmm2 X = " +
hmm2.getX().getX());
System.out.println("DEFAULT_X X = " +
DEFAULT_X.getX());
}
}

Hint: It outputs exactly what the code tells it to! Not much of a hint... It doesn't do what the person wrote it expects it to do though.

Answer: 15 for all three.

Why: Cause the Hmm constructor sets its X reference to the static default object. Thereby the call to set the hmm1 object's X value to 15 actually sets the default value to 15!

Hence, Final Static Objects are the devil!

Who Knew XOR Was So Hard?

nblom — Wed, 29 Jul 2009 16:27:11 +0000

XOR in C++

Final Recommendation:

PLAIN TEXT

// 'a' and 'b' are some sort of integer type.
// the double NOTs coerce to a standard boolean type
// (compiler dependent)
!!a ^ !!b

Thankfully Java is easier
http://www.sap-img.com/java/java-boolean-logical-operators.htm

PLAIN TEXT

// 'a' and 'b' are of boolean type
// yay, no coercion necessary!
a ^ b

I didn’t know that the ^ operator was overloaded to handle Booleans, until I needed it a few weeks ago.

Getting the serialVersionUID Programmatically

nblom — Wed, 11 Feb 2009 16:35:28 +0000

At work I have been tasked with some Java serialization issues and I needed a quick way to get the serialversionUid from a class.

I tried the serialver command that comes with the JDK, but I didn't like that I had to setup the full classpath (which for us can be quite large, lots of jars and directories). Instead I wanted it to work in my Eclipse environment which already has this classpath set and is always updated.

I found this site that had a simple way of doing it:
http://www.jguru.com/faq/view.jsp?EID=42982
Thanks Tim!

I wrote up a little wrapper main function:

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import java.io.ObjectStreamClass;
public class SerialVer {
public static void main(String[] args)
throws ClassNotFoundException {
if(args.length != 1) {
System.err.println("Must pass a class name!");
System.exit(-1);
}
Class cclass = Class.forName(args[0]);
long uid =
ObjectStreamClass.lookup(cclass).getSerialVersionUID();
StringBuffer sb = new StringBuffer();
sb.append(cclass.getName());
sb.append(":\t");
sb.append("static final long serialVersionUID = ");
sb.append(uid);
sb.append("L");
System.out.println(sb.toString());
}
}

Reverse an Array in Place

nblom — Tue, 16 Oct 2007 03:02:59 +0000

I was just looking through some code. I noticed that an array needed to be reversed and that the original order was never needed again. This was a perfect time to reverse the array in place. This was Java so I looked in the Arrays class. But alas there wasn't a reverse for primitive arrays! Java Lists get a reverse method in the Collections class. But primitive arrays get no such love.

Also, I thought of using the asList method from Arrays, but that just seems like a ton of overhead.

So instead I wrote a quick little method for ints and any other primitive type.

Here is the int example:

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public static void reverseInPlace(int[] iar) {
final int length = iar.length;
final int halfLength = length / 2;
final int lengthMinus1 = length - 1;
for (int i = 0; i ) {
final int index2 = lengthMinus1 - i;
//swap
int tmp = iar[i];
iar[i] = iar[index2];
iar[index2] = tmp;
}
}

Basically, this method just swaps the items from the front to back until reaching the middle of the array. If the loop continued on, it would just switch everything back and the original order would be preserved!

The other implementations for the rest of the primitive types can be found here.

onbeforeunload IE7 Woes!

nblom — Fri, 12 Oct 2007 19:40:39 +0000

Was just having a problem getting the IE7 onbeforeunload event to be canceled. Found this blog about it: OnBeforeUnload, IE7, Assigning event handlers to null and the problems that arise.

Pretty simple, just wrap the return with a boolean:

PLAIN TEXT

var goodExit = false;
window.onbeforeunload = confirmExit;
function confirmExit()
{
// normally this if-check wouldn't be here,
// cause the event handler was nulled elsewhere.
// But IE7 doesn't respect the null, and
// wants the handler to not return anything
// (not even null).
if (!goodExit)
{
return "Leaving this page will cause all unplaced orders to be discarded."+
" Are you sure you want to leave the page?";
}
// notice no return statement here!
}
. . . . .
"image" src="<%=AppService.BASEDIR%>/images/lgrequest.gif" onclick="javascript: goodExit = true; window.onbeforeunload = null; document.forms[0].submit();" />

This example was stolen from Brandon Himes and his blog, The Busted Mug. Thank you Brandon!

A Good Reasoning to Nullify an Object!

nblom — Fri, 05 Oct 2007 20:33:04 +0000

If you overwrite a reference with a new object, the object is first created and /then/ the reference is overwritten, which means the object can be only GCed /after/ the new object has been created.

Usually this doesn’t matter. However, if you want to overwrite an object which is so big that it only fits once into the memory, you’ll need to null the reference before creating/assigning the new instance.

Eg:

//FatObject fits only once into memory
FatObject fatty;
fatty=new FatObject();
fatty=new FatObject();

Will bomb with OOME. Whereas…

FatObject fatty;
fatty=new FatObject();
fatty=null;
fatty=new FatObject();

Will be fine, because the second creation of the FatObject will trigger a full GC and the GC will be able to clear enough memory (since the old reference has been nulled).

Well, that rarely matters, but it’s good to know.

Jos Hirth wrote this in response to this post by Jeroen van Erp.

In this post, Jeroen was talking about a long standing bug/issue/misunderstanding of how Strings are handled in Java. The problem that occurs only comes up when taking a substring of a large String. If all that is wanted is the small substring, the substring must be wrapped by a new String call. This will allow the larger String to be garbage collected. Normally when a substring is taken, the underlying char array is shared. This is usually good practice, because it saves memory.

But, and this is a big but, if the substring is taken from a large string, then memory can be leaked, because a lot of memory is wasted in the underlying character array.

Now, why did I quote the above passage from the comment area? Cause I had never thought of the issue Jos brought up. It's interesting to think of an object of which only one can fit in memory. Let alone creating a second!

Changing the Color of a JCheckBox check in a JTable

nblom — Tue, 27 Jun 2006 23:53:13 +0000

Ever wanted to change the color of a JCheckBox in a JTable to the table's foreground color? Now you can!

Example Screenshot:

This is a renderer for Booleans in a JTable.

PLAIN TEXT

import java.awt.Color;
import java.awt.Component;
import java.awt.Graphics;
import javax.swing.JCheckBox;
import javax.swing.JTable;
import javax.swing.table.TableCellRenderer;
/**
* This class implements a boolean renderer for a JTable. It overrides the icon for the CheckBox to draw in the
* foreground color.
*/
public class BooleanRenderer extends JCheckBox implements TableCellRenderer {
public BooleanRenderer() {
super();
setHorizontalAlignment(JCheckBox.CENTER);
setIcon(new ColorableMetalCheckBoxIcon());
}
public Component getTableCellRendererComponent(JTable table, Object value,
boolean isSelected, boolean hasFocus, int row, int column) {
if (isSelected) {
setForeground(table.getSelectionForeground());
super.setBackground(table.getSelectionBackground());
} else {
setForeground(table.getForeground());
setBackground(table.getBackground());
}
setSelected((value != null && ((Boolean) value).booleanValue()));
return this;
}
/**
* Changes the check box check mark to be the foreground color.
* NOTE:This was found here http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4449413 .
*/
static class ColorableMetalCheckBoxIcon extends javax.swing.plaf.metal.MetalCheckBoxIcon {
protected void drawCheck(Component c, Graphics g, int x, int y) {
final Color old = g.getColor();
g.setColor(c.getForeground());
super.drawCheck(c, g, x, y);
g.setColor(old);
}
}
}

This is the corresponding Editor.

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import java.awt.Component;
import javax.swing.DefaultCellEditor;
import javax.swing.JCheckBox;
import javax.swing.JTable;
/**
* This class implements a boolean editor for a JTable. It overrides the icon for the CheckBox to draw in the
* foreground color.
*/
public class BooleanEditor extends DefaultCellEditor {
public BooleanEditor() {
super(new JCheckBox());
JCheckBox c = (JCheckBox) getComponent();
c.setHorizontalAlignment(JCheckBox.CENTER);
c.setIcon(new BooleanRenderer.ColorableMetalCheckBoxIcon());
}
public Component getTableCellEditorComponent(JTable table,
Object value,
boolean isSelected,
int row,
int column) {
JCheckBox c = (JCheckBox) getComponent();
if (isSelected) {
c.setForeground(table.getSelectionForeground());
c.setBackground(table.getSelectionBackground());
} else {
c.setForeground(table.getForeground());
c.setBackground(table.getBackground());
}
c.setSelected((value != null && ((Boolean) value).booleanValue()));
return c;
}
}

Quick and Dirty Tester Program!

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import java.awt.Color;
import java.awt.Dimension;
import java.awt.FlowLayout;
import javax.swing.*;
import javax.swing.table.AbstractTableModel;
import javax.swing.table.DefaultTableModel;
/**
* shows how to use the BooleanEditor and the BooleanRenderer.
*/
public class JTableBooleanTester extends JFrame{
public JTableBooleanTester(){
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
Dimension dim = new Dimension(200,75);
TestTableModel ttm = new TestTableModel();
JTable table1 = new JTable(ttm);
table1.setForeground(Color.WHITE);
table1.setBackground(Color.DARK_GRAY);
JScrollPane sp1 = new JScrollPane(table1);
sp1.setPreferredSize(dim);
JTable table2 = new JTable(ttm);
table2.setForeground(Color.WHITE);
table2.setBackground(Color.DARK_GRAY);
table2.setDefaultEditor(Boolean.class, new BooleanEditor());
table2.setDefaultRenderer(Boolean.class, new BooleanRenderer());
JScrollPane sp2 = new JScrollPane(table2);
sp2.setPreferredSize(dim);
getContentPane().setLayout(new BoxLayout(getContentPane(),BoxLayout.Y_AXIS));
getContentPane().add(sp1);
getContentPane().add(sp2);
pack();
}
public static void main(String[] args) throws Exception {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
SwingUtilities.invokeLater(new Runnable(){
public void run() {
JFrame frame = new JTableBooleanTester();
frame.setVisible(true);
}
});
}
static class TestTableModel extends AbstractTableModel{
Object[][] data = {{Boolean.TRUE, "Testing 1!"},{Boolean.FALSE,"Testing 2!"}};
Object[] names = {"Bool", "Something!"};
public int getRowCount() {
return data.length;
}
public int getColumnCount() {
return names.length;
}
public Object getValueAt(int rowIndex, int columnIndex) {
return data[rowIndex][columnIndex];
}
public void setValueAt(Object aValue, int rowIndex, int columnIndex) {
switch(columnIndex){
case 0:
data[rowIndex][columnIndex] = aValue;
}
fireTableDataChanged();
}
public boolean isCellEditable(int rowIndex, int columnIndex) {
return 0 == columnIndex;
}
public Class getColumnClass(int columnIndex){
return data[0][columnIndex].getClass();
}
}
}